[BC] lightning

[Gary Peterson]

Clive,

Some of the worst lightning/static electricity problems I have ever dealt
with was on a shunt-fed, grounded, half-wave tower with a relatively newly
replaced ground system (120 buried copper radials, ~ 50 m long in a swamp).
When a storm was brewing, fat, blue sparks would jump from the feedthrough
insulator in the wall to almost anything metallic in the transmitter
building (metal shelf with series vacuum tuning cap, lighting conduit,
etc.).  Very unnerving and tough on torroidal coupled RF ammeters!  This
even, sometimes, occurred with dusty, high winds and clear skies.

With the station shut down (on a "quiet" day) there was less than an ohm of
measured D.C. resistance between the shunt-feed wire (attached ~ 50 m up the
tower, IIRC) and the 4" (~10 cm) copper strap attached to the tower
base/ground system.  This measurement was made with the static-drain choke
disconnected.  (Yes, I had added a static-drain choke to the shunt-feed
wire, which seemed to do little good.)

I spent lots of time at two other series-fed AM sites, each within two miles
of the above mentioned site and never saw static discharges anywhere near as
spectacular or detrimental to clean underwear.

>From my limited experience, the belief that shunt-fed towers have fewer
lightning problems is a myth.

Gary, K?CX
CE KFXS/KOUT/KKMK/KRCS/KKLS/KBHB/KIMM
Rapid City/Sturgis, SD

"Seems like another recommendation to use grounded antennas like the shunt
fed.
NO lightning problems at all since the structure is solidly attached to the
earthing radials.

Clive"